Dry disconnect couplings, also commonly called dry-break couplings, are used in various applications to connect one fluid conduit to another to form a continuous flow path. Typically, dry disconnect couplings comprise a receptacle and a coupler. The receptacle may be mounted on a fluid conduit, or may form the inlet to, or outlet from, a fluid container such as a storage tank. The coupler may be mounted on a fluid conduit and means are provided for mechanically locking the coupler and receptacle together to provide an environmentally sealed connection for the transfer of fluids.
The receptacle and coupler each have a flow passageway, which is sealed by a poppet valve when the coupling is uncoupled. When the coupler is locked on to the receptacle, the poppets are displaced from their seats to permit flow of fluid through the coupling. Mechanical interlocks are provided to prevent separation of the two components unless the poppets are returned to their closed position. There are many designs of dry disconnect couplings in existence. Examples of such couplings are those disclosed in U.S. Pat. No. 5,273,071 issued to David A. Oberrecht and U.S. Pat. No. 5,628,344 issued to Robert D. Roberts.
As the name implies, dry disconnect couplings used in liquid transfer operations are intended to prevent spillage of liquid when the two components of the coupling are uncoupled. In practice, some small quantity of liquid is spilled each time the coupling is disconnected. Oberrecht states that prior disconnect couplings of this type, used in a four inch conduit, can limit the loss of liquid to something of the order of 2/3 of an ounce for each disconnection and as he points out, this can result in potentially hazardous soil contamination over an extended period of use. Various authorities can be expected to attempt to regulate this environmental risk. For example, a draft of an Association of American Railroads Locomotive Fueling Interface Standard requires that the liquid spilled during a disconnect of a three inch coupling when tested shall be less than 5 cubic centimeters (i.e. 1/6 fluid ounces) for each test.
The primary source of spillage is the liquid remaining in the annular space between the periphery of the poppets and the circumferential seal between the coupler and the receptacle, when the poppets are retracted to the closed position. A secondary source of spillage is liquid, which may enter into the space between the opposed faces of the poppets when they are displaced in the open position and which remains there when the poppets are retracted. This space is the result of misalignment between the poppet faces, manufacturing imperfections, or damage to the poppet faces, or a combination of these causes. Oberrecht provides an O-ring mounted in a groove formed in the face of the coupler poppet which forms a seal against the face of the receptacle poppet to prevent the interface being wetted when the poppets are in the open position. Liquid residue may still remain around the periphery of this seal. Oberrecht also reveals an alternative method in which a sealing ring of rectangular cross section is bonded to the face of the coupler poppet with the purpose of minimizing the annular gap around the periphery of the poppet. The cross section of this seal is much less resilient than the O-ring and is less suitable for the function desired. Furthermore, being bonded in place, it is difficult to replace when this becomes necessary. Roberts accepts the aforementioned deficiencies and provides a reservoir to collect any spillage and a means to return it to the flow path. It will be noted that this return flow is induced by the passage of liquid through the coupling and ceases when the poppets are closed.